L. Edwall

Ultrastructure of nerves in the dentinal-pulp border zone after sensory and autonomic nerve transection in the cat

In order to investigate the origin of intradentinal nerve-like structures, unilateral transection of the sensory (inferior alveolar nerve) and/or the autonomic (cranial cervical sympathetic ganglion) supply was performed in 6 cats. After 2—4 weeks, when degenerative change was expected in the cut nerves, electrophysiological recordings from the dentin showed total absence of impulse activity in teeth subjected to sensory denervation regardless of whether or not the autonomic innervation was intact. Control teeth, on the other hand, responded to different local pain stimuli. Electron microscopic study of predentin and inner dentin in control teeth showed intratubular nerve-like structures similar to «associate cells» earlier described in human teeth. In teeth subjected to sensory nerve resection, however, the intradentinal «associate cells» showed advanced degenerative change or were absent. Resection of the sympathetic nerve supply did not influence the appearance of these intratubular structures.The pres...

Perception of pulpal pain as a function of intradental nerve activity

&NA; The purpose of the present investigation was to find neurophysiological correlates of pain perception. The magnitude and time course of perceived pain was successfully related to the neural discharge evoked by rapid cooling of the tooth surface in 6 dental patients whose lower incisors were to be extracted for prosthodontic reasons. Two cavities were prepared on the facial surface of human lower incisors. The cavities were deepened using hand driven instruments until the pulp was visible through a thin layer of dentin. A metal tube was placed in contact with amalgam on each cavity bottom and fixed in place by composite filling material. The tubes were connected to standard equipment for electrophysiological recordings by a flexible circuit. The magnitude of perceived pain was assessed by a cross‐modality matching to finger span in combination with sensory verbal pain descriptors and magnitude estimation. The striking agreement between the integrated nerve activity, probably of the A&dgr; type and pain perception, is of great importance from the methodological point of view since it strongly argues in favor of the appropriateness of the techniques applied here to elucidate the neural substrate of some types of nociception and also to evaluate various means of relieving such pain.

Involvement of afferent nerves in pulpal blood-flow reactions in response to clinical and experimental procedures in the cat

A unilateral resection of the mandibular nerve (n = 20) was made 10-14 days before investigation of the contribution of afferent nerves in vasodilator reactions in the dental pulp. Lower canine teeth were subjected to various stimuli and pulp blood-flow responses monitored by laser Doppler flowmetry. An absence of response to bipolar electrical (5 impulses, 50 microA, 5 ms, 2 Hz) stimulation on the tooth surface was used to demonstrate a successful chronic nerve lesion. Local application of capsaicin (10(-4) M) in a deep dentinal cavity induced a long-lasting increase in pulpal blood flow in control teeth only. Bradykinin (10(-3) M) induced significantly larger responses in control than in denervated teeth (58.3 +/- 9.8% and 24.5 +/- 4.9%, respectively, p less than 0.005, n = 8); in addition, the onset was slower and the duration of the response significantly (60%) shorter than in control teeth. Intermittent grinding of surface dentine instantly increased flow in control teeth by 53.0 +/- 12.5% (n = 12) whereas in denervated teeth the response was delayed and significantly (70%) smaller. Deeper preparation produced responses of similar magnitude in control and denervated teeth (69 and 50%, respectively) but the onset was delayed in denervated teeth. Low-intensity ultrasonic stimulation caused vasodilation in intact teeth (38% increase) but had no effect in denervated teeth. This effect was abolished after local anaesthetic (mepivacaine) injection. Sympathectomy (n = 3) did not influence stimulation-induced blood-flow responses in the dental pulp.(ABSTRACT TRUNCATED AT 250 WORDS)

The diameter and number of dentinal tubules in rat, cat, dog and monkey: A comparative scanning electron microscopic study

The aim of the study was to investigate in commonly used experimental animals the pulpal wall and the dentin with special reference to the number and diameter of the dentinal tubules. The coronal dentin of a total of 26 permanent, intact teeth from rat, cat, dog and monkey was fractured experimentally. The calculations were based on the study of about 150 scanning electron microscope (SEM) photographs of fractured surfaces and of the pulp chamber wall. The number of dentinal tubules per unit area was calculated and the tubule diameter was measured at various distances from the pulp. The tubules were found to be widest at the pulpal wall, where the mean diameter ranged form 1.7 to 2.8 mum, the highest value being found in monkey and the lowest in the incisors of rat. In the middle part of the dentin the mean diameter varied from 1.0 to 1.3 mum and at the periphery it was 0.6 to 0.9 mum. The largest number of tubules per unit area was found immediately incisal of the pulp horn and the smallest number cervically, near the enamel. At the pulpal wall the mean number of the tubules ranged from 50,000 to 90,000/mm2, in the middle of the dentin it was between 37,000 and 50,000/mm2 and at the periphery it was between 10,000 and 25,000/mm2. In all species examined the dentinal tubules showed a straight course, except in incisors of rat, where local irregularities were seen. A comparison was also made between the species studied and homo with respect to the number and width of the dentinal tubules.

A new technique for recording of intradental sensory nerve activity in man

&NA; A technique was developed to record intradental sensory nerve activity in man. The method involves permanent fixation of electrodes in dentin thus enabling continuous recordings to be made. Acute as well as long term influences on excitability of sensory nerve endings in the tooth can thus be studied. A coincidence between recorded spike activity and pain sensation was observed.

Differential effects of nitric oxide synthesis inhibition on basal blood flow and antidromic vasodilation in rat oral tissues.

The role of nitric oxide in the mediation of (a) antidromic and (b) substance P-induced vasodilation in the pulp, lip, oral mucosa and submandibular gland was investigated in anaesthetized rats by means of laser Doppler flowmetry. Bolus or continuous infusion of N omega-nitro-L-arginine methyl ester (L-NAME) increased mean arterial blood pressure and reduced basal blood flow in the pulp but not in the lip. Electrical stimulation of the inferior alveolar nerve, in the presence of phenoxybenzamine, resulted in a long lasting vasodilation in lower lip and incisor pulp. Infusion of L-NAME enhanced the antidromic vasodilation in both lip and pulp. Pretreatment with L-arginine prevented these effects. Administration of the enantiomer (D-NAME) did not exert any effect on basal blood flow and on antidromic vasodilation. Infusion of substance P resulted in a transient vasodilation in all of the oral tissues studied. L-NAME reduced this vasodilation in the submandibular gland (only the lower doses) but it potentiated the responses in the pulp and oral mucosa. Pretreatment with L-arginine prevented the potentiated responses in the pulp and those induced by the lower doses of substance P in the oral mucosa. Thus, nitric oxide appears to differentially regulate the basal blood flow and the antidromic or substance P-induced vasodilation in the microvasculature of the lip and dental pulp.

Influence of vasodilator substances on pulpal blood flow in the cat

The objective of the study was to determine the response in the pulpal blood flow to vasodilator substances at different levels of vasomotor tone.Simultaneous determinations of iodide disappearance rate (k-value) from dentinal cavities and, as control, from the adjacent alveolar submucosa were performed on anesthetized cats. Changes in k-value reflected changes in blood flow. Close i.a. infusion of acetylcholine, histamine and bradykinin did not influence pulpal microcirculation when the sympathetic nervous tone was low. At a higher level of nervous vascular tone, obtained by direct electrical stimulation of the cut sympathetic cervical trunk, the substances were shown to increase the pulpal blood flow. Papaverine and warming had a more pronounced vasodilator influence on pulpal blood flow, suggesting the presence of a local myogenic vascular tone regulating the exchange function, which was unaffected by acetylcholine, histamine and bradykinin. These substances were thus shown to act as inhibitors of symp...

Evans blue extravasation in rat dental pulp and oral tissues induced by electrical stimulation of the inferior alveolar nerve.

Whether increased extravasation of plasma protein may occur in the rat incisor pulp as a result of antidromic stimulation of afferent nerves was investigated, and this preinflammatory reaction compared with that in adjacent soft tissues. In anaesthetized rats, the inferior alveolar nerve was exposed and stimulated electrically (10-15 V, 2 ms, 10 Hz for 30 s or 5 min). Blood flow changes in the lower lip and incisor pulp were recorded by laser Doppler flowmetry. Increased vascular permeability in the lip, gingiva and pulp was indirectly determined by means of the Evans blue dye method and spectrophotometric analysis. Stimulation of the inferior alveolar nerve for 30 s, in the presence of the alpha-adrenergic blocker phenoxybenzamine (3 mg/kg), increased blood flow in the lip by 172 +/- 16% and in the pulp by 38 +/- 5% as compared to basal blood flow. Intravenous (i.v.) administration of atropine (1 mg/kg), chlorisondamine (3 mg/kg), timolol (150 micrograms/kg), cimetidine plus mepyramine (3 mg/kg of each), methysergide (1 mg/kg) and diclofenac sodium (3 mg/kg) was without effect on this response. Acute pretreatment with capsaicin (1-3 mg/kg, i.v.), however, abolished the vasodilation in the pulp and reduced that in the lip by 58% (p < 0.05). In untreated animals, stimulation of the inferior alveolar nerve for 5 min increased the Evans blue content in the ipsilateral lip by 164% (p < 0.001), gingiva by 55% (p < 0.01) and pulp by 67% (p < 0.01). Pretreatment (i.v.) with a combination of cimetidine and mepyramine counteracted the dye extravasation only in the gingiva.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of sympathetic fibres in the pulp by electrical stimulation of rat incisor teeth

Previous studies of the sympathetic nerve supply of the rat mandibular incisor pulp have shown conflicting results. Here, the neurovascular control of the rat lower incisor pulp was investigated by stimulating the tooth crown and the cervical sympathetic trunk electrically and monitoring blood-flow changes in the pulp by laser Doppler flowmetry. In addition the presence of noradrenaline (NA) in the pulp and gingiva was examined biochemically in untreated and sympathectomized animals by high-performance liquid chromatography. The tissue concentrations of NA in the pulp were 11-fold greater than those of gingiva. Surgical sympathectomy significantly reduced the NA content in the pulp by 76%. Monopolar electrical stimulation of teeth (25-50 microA) for 1 min resulted in a frequency-dependent reduction followed by an increase in pulpal blood flow. At 16 Hz the reduction in blood flow was 65% and the subsequent increase was 9%. After intravenous administration of the alpha-adrenoceptor antagonist phentolamine, the stimulation-induced reduction in pulpal blood flow was diminished by 94% while the increase was significantly enhanced (from 9 to 40%). Infusion of the beta-adrenoceptor antagonists propranolol and timolol significantly reduced this increase in blood flow by 53 and 55%, respectively. Preganglionic sympathetic nerve stimulation also induced a frequency-dependent reduction followed by a slight increase in pulpal blood flow. This reduction in blood flow was almost abolished after alpha-adrenergic blockade and there was no subsequent increase. These findings suggest that there are sympathetic nerve fibres in rat incisor pulp and that they are activated upon monopolar electrical stimulation of teeth resulting in alpha- and beta-adrenoceptor mediated blood-flow responses.

Relation between intradental nerve activity and estimated pain in man--a mathematical model.

Abstract Intradental nerve activity (INA) induced by cold stimulation of human teeth is regularly accompanied by pain perception. In this study a mathematical model was developed in order to quantify the relationship between INA and pain. In 5 patients (45 experiments) INA was recorded using electrodes implanted in lower incisor teeth. Brief cold stimulations induced bursts of INA. The intensity of the resulting pain was simultaneously evaluated by means of an intermodal matching technique, finger span. The relationship between perceived pain and the integrated INA was analyzed using various mathematical operations (inter alia Fourier analysis) by means of a computer. A transfer function which describes the pain response following INA was found. This preliminary mathematical model, which is characterized by 5 parameters, consists of 2 parts, one which responds to fast changes in the afferent nerve signal, and another which reacts with a delay. The validity of the model has been tested, and it was found that the model consists of an adequate number of parameters and their cross‐interaction is low. The analysis indicates that the parameters which determine the pain response following INA can be quantified and that they might be used as a measure of the efficacy of various pain relieving procedures.